It is becoming increasingly important to minimize vibration in a helicopter. Stringent requirements exist if crew and passenger comfort are to be present. The life of structural components and electronic equipment is greater with minimized vibration provided by special mounting structures. In military aircraft, the presence of armaments and the necessity for accurate fire control make stabilization of the aircraft and minimization of aircraft vibration important.
Heretofore, at least one project was directed at reducing vibration by using modal shaping. Such effort was based on the goal of reducing vibration levels in forward flight by modifying the mass distribution and to a lesser extent the stiffness distribution of the blade by using a modal shaping parameter. In another project, vertical hub shears due to blade flap-wise bending were minimized using mathematical programming techniques. Both programs were said to be based upon simple linear models for blade vibration employing modal analysis and the principles of super-position. Some findings indicate that mere addition of mass to the tip of the blade produces beneficial changes in the modal shaping parameter. The concept of vibration reduction by adding tuning masses has been used in rotor design prior hereto. In a further effort, non-structural tuning masses added to the outboard segments of the blade determined in an automated manner by a structural optimization process.
From the foregoing, it is apparent that there is a demand for further reduction of vibration.